A068007 Least number k such that the number of primes of the form [k/j] for j=1..k (A068050) is n, or zero if impossible.

1, 2, 5, 7, 10, 11, 15, 21, 0, 22, 23, 31, 34, 38, 35, 45, 50, 46, 47, 53, 62, 58, 59, 67, 69, 84, 70, 71, 79, 83, 87, 92, 93, 101, 94, 105, 95, 106, 107, 116, 117, 122, 118, 125, 119, 134, 135, 139, 146, 142, 149, 143, 156, 155, 158, 159, 171, 166, 167, 176, 175, 185

Offset: 0

Author

Robert G. Wilson v, Feb 12 2002

Keywords

• nonn

Comments

a(n) = 0 for n = 8, 94, 103, 122, 180, 283, 311, 353, 355, 398, ...

Crossrefs

Cf. A068050.

Programs

Mathematica

f[n_] := Count[ PrimeQ[ Floor[ n/Table[i, {i, Floor[n/2]} ]]], True]; a = Table[0, {100} ]; Do[b = f[n]; If[b < 100 && a[[b + 1]] == 0, a[[b + 1]] = n], {n, 1, 300}]; a

Extensions

Name corrected by Sean A. Irvine, Jan 18 2024